iqi2] " CURRENT LITERATURE 171 



Geotropism.— Ritter^ applies the rotation method of Piccard^ for 

 determining the distribution of geotropic sensitiveness in various grass seed- 

 lings. Ritter states that it is through the application of this brilliant con- 

 ception alone that the distribution of geotropic sensitiveness has been settled 

 in some cases. 5 In Avena saliva, Hordeum vulgare, and Phalaris canariensis, a 

 short tip zone of the coleoptile is very much more sensitive than the basal 

 region, which shows some geotropic sensitiveness. In Avena the very sensitive 

 zone is 3 mm. long, and in Hordeum and Phalaris 4-5 mm. In Set aria italica 

 all regions of the coleoptile are equally sensitive, while in Sorghum vulgare the 

 tip region shows slightly greater sensitiveness. Since the main curving is in 

 the epicotyl, a conduction of the stimulus to that region from the coleoptile 

 must occur. The distribution of the motile starch in all these organs cor- 

 responds closely with the distribution of geotropic sensitiveness, so that 

 Ritter considers the work confirmatory of, or at least not antagonistic to, the 

 statolith starch theory. 



In a study of the geotropism of rhizoids carried out in Haberlaxdt's 

 laboratory, Bischoff 6 comes to the following conclusions: The rhizoids of the 

 growing gemmae of Marchantia polymorpha and Lunularia cruciata are, con- 

 trary to the conclusion of Weinert, positively geotropic, and those of the thalli 

 show the same character with lower sensitiveness. Bischoff asserts that the 

 lack of motile starch in these rhizoids does not necessarily argue against the 

 statolith theory, for other motile bodies may take its place. The rhizoids of 

 ferns are ageotropic. The main rhizoid of mosses {Br yum capi/lare, B. 

 argenteum, and Leptobryum pyriforme) is positively geotropic in light, while 

 the protonemata and side rhizoids are ageotropic. In the mosses statolith 

 starch is found in the main rhizoid. 



Jost and Stoppel 7 have established the interesting fact that under high 

 centrifugal force of sufficient duration the roots of Lupinus give the negative 

 geotropic response instead of the positive. For negative response 16 gravities 

 or more are needed for decapitated roots, and 70 gravities or more for intact 

 ones. This lines geotropic response up with Oltmann's findings for heliotropic 

 response; one and the same organ responds either positively or negatively, 

 depending upon the strength of the stimulus. Parallel with heliotropism a 



3 Ritter, Herman von Guttenberg, Uber die Verteilung der geotropischen 

 Empfindlichkeit in der Koleoptile von Gramineen. Jahrb. Wiss. Bot. 50:289-327. 

 fig- f* 1912. 



4 Pfeffer, W., Physiology. English ed. 3:418-419. 1905. 



5 See review of Darwin in Bot. Gaz. 46:387. 1908; also review of Haberlandt 

 in Bot. Gaz. 47:482-483. 1909. 



6 Bischoff, Hans, Untersuchungen liber den Geotropismus der Rhizoiden. 

 Beih. Bot. Centralbl. 28:94-133. 1912. 



7 Jost, L., and Stoppel, R., Studien uber Geotropismus. II. Die Veranderung 

 der geotropischen Reaktion durch Schlenderkraft. Zeitsch. Bot. 4:207-229. 1912. 



